1. Field of the Invention
This invention relates to a catalytic process for oxidative polymer degradation. More particularly, it is concerned with the reduction of molecular weight and the thickening efficiency of primary oil soluble hydrocarbon polymers, such as hydrogenated random copolymers and block copolymers of styrene-isoprene or styrene-butadiene, polyisobutylene, poly-n-butene, low unsaturation butyl rubber, low unsaturation ethylene-propylene-diene terpolymers (EPDM's), or ethylene-alpha-olefin copolymers, and preferably ethylene-propylene copolyemers, of the type which are to be used as viscosity index improver additives or as precursors for dispersants and multi-functional viscosity index improver additives for lubricating oil compositions.
2. Description of the Prior Art
Copolymers of ethylene and an alpha-olefin, such as a C.sub.3 -C.sub.28 alpha-olefin, and particularly copolymers of ethylene and propylene, and their preparation are widely described in the art. Typical descriptions will be found, for example, in U.S. Pat. Nos. 3,300,459; 3,687,849; 3,687,905; 4,116,636; and 4,137,185.
It is known that olefin and diolefin homopolymers and ethylene-alpha-olefin copolymers may be degraded or depolymerized, thereby reducing the molecular weight thereof. Such degradation is known to be accomplished, for example, by shear assisted oxidation of the polymers and copolymers in air in a mechanical mixer, such as in extruder, masticator, Banbury mixer, rubber mill, or the like, and by heating the polymers and copolymers, sometimes in the presence of air. One such degradation process, which is described in U.S. Pat. No. 3,313,793, involves (a) the formation of a solution of a conjugated diene polymer, (b) combining therewith a peroxide and a copper source such as copper, a copper halide or a copper carboxylate, (c) heating the resulting mixture in the substantial absence of oxygen, and (d) recovering a diene polymer product having a substantially reduced average molecular weight.
U.S. Pat. No. 3,332,926 relates to the thermal degradation of polyolefins, including ethylene-propylene copolymers, to produce relatively low molecular weight polymers which are useful, for example, as wax substitutes, blending agents, coating compositions and, in general, in fields where hydrocarbon resins and waxes find utility. The process described in that patent comprises mixing a crystalline starting polymer with from 0.075% to 10% by weight of a metal salt of carboxylic acid and heating the mixture in an atmosphere which is substantially free from oxygen to a temperature of about 275.degree. C. to 450.degree. C., until a substantial reduction in the molecular weight of the polymer takes place.
U.S. Pat. No. 3,316,177 discloses a functional fluid containing a sludge inhibiting detergent comprising the polyamine salts of the reaction product of the maleic anhydride and an oxidized interpolymer of propylene and ethylene. The interpolymers from which the oxidized, degraded interpolymers are derived usually have molecular weights of at least about 50,000. The interpolymers are oxidized and degraded by heating them at a temperature of at least about 100.degree. C. in the presence of oxygen or air. Such degradation usually is characterized by a substantial reduction of the molecular weight of the interpolymer.
U.S. Pat. No. 3,345,352 relates to a catalytic process for the thermal degradation of the polyolefins, including copolymers of ethylene and propylene. The degradation process involves heating a mixture of a crystalline polyolefin and an oxide or carbonate of an alkali metal, alkaline earth metal, or certain selected transition metals such as copper, iron, titanium, vanadium, etc. in an atmosphere substantially free of oxygen to a temperature of from 275.degree. C. to 450.degree. C. for a minimum time period of at least five minutes.
U.S. Pat. No. 3,687,849 relates to lubricants containing oil-soluble graft polymers derived from degraded ethylene-propylene interpolymers. The interpolymers from which the degraded polymers are derived usually have a molecular weight of about 50,000-800,000, and the degraded interpolymers are prepared by heating the interpolymer, or a fluid solution of such interpolymer, in an inert solvent, at a temperature of at least about 140.degree. C. in the presence of oxygen or air. The degradation of the interpolymer is characterized by a substantial reduction of its molecular weight. A similar disclosure is set forth in U.S. Pat. No. 3,687,905.
U.S. Pat. No. 3,769,216 relates to novel polymers which are produced by reacting a primary or secondary amine and a mechanically degraded, oxidized atactic ethylene propylene copolymer, and to automotive lubricating oils containing such polymers as antivarnish additives. The ethylene propylene copolymer is mechanically degraded in the presence of oxygen and in the absence of any solvent in a closed vessel equipped with shearing blades. A typical apparatus of this type is described as a device containing counter-rotating helical blades and known as a "Brabender Torque Rheometer."
U.S. Pat. No. 4,089,794 discloses ethylene copolymers derived from about 2 to 98 wt % ethylene, and one or more C.sub.3 to C.sub.28 alpha olefins, for example ethylene-propylene, which are solution-grafted with an ethylenically unsaturated carboxylic acid material, and thereafter reacted with a polyfunctional material reactive with carboxyl groups. The resulting polymers are useful as dispersant additives for lubricating oils and hydrocarbon fuels, and as multifunctional viscosity index improvers if their molecular weight is above 10,000.
U.S. Pat. No. 4,113,636 discloses the mechanical degradation at elevated temperatures, and in the presence of air or oxygen-containing gas, of copolymers comprising about 68 to 80 mole % ethylene and one or more C.sub.3 -C.sub.8 alpha-olefins to form an oxygenated-degraded polymer which is then reacted with an amine compound. The resulting aminated polymers are useful as viscosity index improving additives.
U.S. Pat. Nos. 4,074,033 and 4,201,732 relate to a process for improving the processability for high molecular weight neoprene polymers. The process comprises treating a solution of the polymers in an organic solvent with an organic peroxide, in the presence of oxygen, to reduce the molecular weight of the neoprene and to lower the viscosity of the solution. The process may be conducted at room temperature with or without agitation, and an accelerator such as a cobalt salt or other transition metal salt may be employed.
The above and other prior art processes thus disclose the degradation of polymers, including ethylene-propylene copolymers, which are to be used as viscosity improver additives or dispersant additives in lubricating oil compositions. However, the speed with which the prior art processes accomplish the degradation and consequent reduction of molecular weight is often sluggish, the cycle time is undesirably high, and the cost is generally high.